MACHIAS — Ten thousand years ago, when the glaciers over Maine receded, some of the first plants to appear were wild blueberry bushes.

“Blueberries are very good at growing in poor, stressful environments,” according to David Yarborough, the University of Maine’s wild blueberry expert.

By the time the Native Americans were harvesting the berries 1,000 years ago, they had discovered that blueberries were not only tasty but also healthy. They also began the practice of burning the fields to kill off unwanted insects and weeds.

In the early 1800s, European settlers gathered berries as a public privilege on the barrens in Washington County.

But wild blueberries remained a purely local crop until the Civil War.

“There was a huge demand for fruit for the Union troops,” Yarborough said, and Down East blueberry growers began shipping boxes of berries by rail.

When asked how today’s growers can call the berries wild when they are so highly farmed, Yarborough said, “We didn’t plant them. We manage them.”

Wild blueberry plants occur naturally in the understory of the Down East forests. The plants send out underground stems or rhizomes. An original plant can cover 75 to 250 feet. New plants may be propagated by seed, softwood cuttings, rhizome cuttings or by digging up sod pieces.

Yarborough said it takes 50 years to establish a good wild blueberry field, and there are 6.5 million varieties of blueberries.

It’s that diversity that gives the wonderful flavor to wild blueberries, he said. “It’s actually a complex mixture of flavors.”

Maine is the largest producer of wild blueberries in the world, and they are grown on 60,000 acres. Six companies operate processing plants that freeze and can berries, and there is one fresh pack cooperative. Ninety-nine percent of Maine’s crop is frozen and most is used as a food ingredient. Less than 1 percent is sold fresh.

Late in July and early August, thousands of hand rakers join mechanical harvesters to bring in the berries. Last year, Maine’s harvest was 88 million pounds with a value of $160 million.

Wild blueberries have the highest antioxidant capacity per serving, compared with more than 20 other fruits.